Add ddescribe, iit for exclusive suites,specs

All this work is part of pivotal/jasmine/pull/181. That pull request is almost a year old, however, and needed some tweaks to work on master.

When any ddescribe is registered, only specs withing these exclusive suites will be run

```javascript
describe('normal', function() {
  ddescribe('exclusive', function() {
    // all specs here will be run
  });

  // nothing here will run
  it('should not run', function() {});
});
```

When any iit is registered, only these exclusive specs will be run (precedence over ddescribe)

```javascript
it('should not run', function() {});
iit('should run', function() {});
it('should not run 2', function() {});
iit('should run as well', function() {});
```

We've been using this feature for quit a while during development of AngularJS.

It's part of Jasmine - JsTD adapter, I think it was originally an idea of @IgorMinar.

I really miss this feature when using jasmine-node or when using SlimJim.

I think, it really should be part of the core, so I did implement it.